In the prior art, there have been attempts to achieve a substantially flat top or pseudo flat top wave front or beam for use in a drilling or otherwise forming a blind via, hole, an aperture or other desired formation in a surface to be processed. One such pseudo flat top wave front or beam is generally shown in FIG. 1 of the drawings and this type of beam generally, when striking a surface to be processed, forms a blind via or aperture therein which has a shape generally depicted in FIG. 2 of the drawings. The problem with this type of blind via or aperture is that a depth of the blind via or aperture tends to be deeper around the perimeter of the via than it is in the center. This non uniformity results in a blind via or aperture which may be unacceptable for some manufacturing operations or processes.
The inventor believes that one of the problems associated with flat top or pseudo flat top wave fronts or beams is that edge diffraction occurs as the wave front or beam strikes or contacts the surface to be processed. This edge diffraction has a tendency to increase the drilling depth of the blind via or aperture around the perimeter thereof and this results in a blind via or aperture which has an undesirable contour or profile. As can be seen in FIG. 1, a well known laser beam 2, with a fat top or pseudo flat top wave front 4, is diagrammatically depicted. This type of laser beam 2 has an intensity “I” and a diameter “D” and is typically used for drilling and forming holes in objects. However, one major problem with the laser beam 2, when drilling a blind hole in a desired object, for example, is the formation of an uneven base surface 6 at the bottom of the blind via 8. This uneven base surface 6 is generally shown in FIG. 2.
The perimeter region 10 of the blind via 8 is cut significantly deeper than a central region 12 of the blind via 8 thus creating the uneven base surface 6. This defect may increase manufacturing time, result in an improper fit of a desired component, or even possible rejection or discarding the object 14. All of these scenarios ultimately increase the associated manufacturing and assembly costs and are to be avoided. Therefore, the flat top wave front 4 is generally unacceptable for many manufacturing applications, especially when close tolerances are required.